A number of electrochemical sensing techniques for detecting the presence of a metal ion in a sample are dependant on the adsorption of the metal ion on a working electrode. In such techniques, typically the oxidation or reduction of the metal ion can only take place when the metal ion is adsorbed on the electrode. However, many metal ions do not adsorb efficiently on electrode surfaces, in particular carbon surfaces. Electrochemical sensing of the presence of such metal ions can therefore be unreliable, especially where the metal ion is present in the sample only in small amounts. Particular difficulties are experienced when the adsorption of the metal ion on the electrode is in competition with binding to another substance in the sample to be tested.
A new technique is therefore required which addresses the difficulties of poor adsorption of metal ions on electrodes.